Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 230230

Area Forecast Discussion
National Weather Service State College PA
1030 PM EDT Sun Oct 22 2017

Low pressure over the Mississippi Valley will track northward
through the Great Lakes late Monday and Tuesday. A trailing
cold front will push through Pennsylvania Monday night into
early Tuesday. An upper level trough will then swing through
Pennsylvania Wednesday and Thursday.


Ridging at the surface and aloft will remain along the east
coast tonight, ensuring a continuation of fair weather across
the area. A southerly breeze, combined with a thin cirrus
shield, should result in a milder night than those recently.
A blend of latest model guidance supports overnight lows
in the low to mid 50s.

Although there should be enough of a breeze to preclude fog
issues over the bulk of central Pa, a weaker gradient across
southeast Pa could lead to some fog across the southeast part
of the forecast area early Monday morning.


An upper level trough low swinging through the upper midwest
will absorb a closed upper low over the lower Mississippi
valley during the day Monday. This will bring an extensive
plume of moisture into the state from the south.

The south to serly llvl flow will freshen by about 10 kts
during the day Monday and bring with it areas of low clouds
(stratus/Stratocu) and perhaps some patchy drizzle across the
central third of the state.

Despite thickening cloud cover, temps will remain well above
seasonal normals Monday in region of warm advection ahead of
approaching cold front. A blend of latest model guidance
supports maxes in the upper 60s to low 70s. Short to mid range
models continue to narrow in on the timing of the approaching
system. 12Z GEFS and NAM are in fair agreement on showers
reaching Western PA and the Alleghenies late tomorrow afternoon.


Cold front is progged to push slowly east across the
Commonwealth Monday night into early Tuesday. Models showing a
bit of instability ahead of front, which could result in a few
embedded tsra as the NCFRB moves through Mon night.

Surface ridging indicated over central Pa by med range guidance
late Tuesday through Friday, indicating dry weather for most of
the forecast area. The exception will be late Wed, when passage
of shortwave could produce a few showers across the northwest
mountains. Ensemble mean 925/850 temps are slightly below
normal Wed/Thu, likely translating to max temps from the upper
40s over the Alleghenies, to the upper 50s across the southeast
counties. This cooler stretch will be short lived as heights
and 850 temps rise quickly into next weekend.

Another chance for precipitation will arrive at the end of the
period when a cold front is anticipated next Sunday, bringing
rain showers to the region.


Expect most of the night to be VFR. Model data shows
lower visibilities and CIGS late, which may linger into
late morning or early afternoon on Monday. Not sure it
will occur, as no real cold air in place, but slight
southeast flow late, with leading edge of higher dewpoints
working in, left fcst close to what the 18Z package had.

Main change was to bring in lower conditions a tad faster in
some spots, and linger it a hour or so later in some spots.

Expect most of the day to be dry. Some showers possible
late, just have showers in far west around sunset.

LLWS possible far west toward sunset, so have it in for
BFD and JST.

Earlier discussion below.

Guidance continues to show risk for low clouds and fog
developing late tonight into early Monday morning across the
eastern 1/3 of the airspace - and have increased and spread
MVFR/IFR restrictions through the eastern and central TAF sites.
Have kept restrictions until around 14Z. LLWS is possible at
JST/AOO and BFD but it is marginal as strongest low level jet is
above 2KFT. So have left it out of the TAFs for now.


Tue...LLWS/gusty/heavy showers in the morning. Sharp FROPA and
windshift. Improving conditions by afternoon.

Wed-Thu...Sct showers and low cigs possible KBFD/KJST.

Fri...Mainly VFR.


Month-to-date, October 2017 remains the 2nd and 3rd warmest
on record at Williamsport and Harrisburg respectively.




NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald/Lambert
LONG TERM...Lambert/Gartner
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